Guards: Use unique aggregate.

Author: aschackmull

shared/controlflow/codeql/controlflow/Guards.qll

@@ -640,10 +640,11 @@ module Make<
       Guard guard, GuardValue v, SsaPhiDefinition phi, Expr input
     ) {
       exists(GuardValue dv, SsaExplicitWrite inp |
-        guardControlsPhiBranch(guard, v, phi, inp) and
-        // The `forall` below implies that there's only one such `inp` guarded by `guard == v`,
-        // but checking this upfront improves performance of the `forall` check.
-        1 = strictcount(SsaDefinition inp0 | guardControlsPhiBranch(guard, v, phi, inp0)) and
+        // The `forall` below implies that there's only one `inp` guarded by
+        // `guard == v`, but checking this upfront using `unique` as opposed to
+        // merely stating `guardControlsPhiBranch(guard, v, phi, inp)` improves
+        // performance of the `forall` check.
+        inp = unique(SsaDefinition inp0 | guardControlsPhiBranch(guard, v, phi, inp0)) and
         inp.getValue() = input and
         dv = v.getDualValue() and
         forall(SsaDefinition other | phi.hasInputFromBlock(other, _) and other != inp |
@@ -744,7 +745,7 @@ module Make<
       possibleValue(v, false, e, k) and
       not possibleValue(v, true, e, k) and
       // there's only one expression with the value `k`
-      1 = strictcount(Expr e0 | possibleValue(v, _, e0, k)) and
+      e = unique(Expr e0 | possibleValue(v, _, e0, k)) and
       // and `v` has at least two possible values
       2 <= strictcount(GuardValue k0 | possibleValue(v, _, _, k0))
     }